Photometric device.



I. G. PRIEST.

PHOTOMETRIG DEVICE.

APYLIOATION FILED JUNE zo, 1913.

Patented Sept. 2,1913.

UNITED STATES PATENT oEEIcE.

i IRWIN G. PRIEST, 0l' WASHINGTON, DISTRICT 0F COLUMBIA.

PHOTOHETBIG DEVICE.

Speciiestion of Letters Pete-nt.

Patented Sept. 2, 1913.

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To all 'whom it may concern.' l

Beit'known'that I, IRWIN G; Pams'r, a citizen of the United States, and resident of Washington, District of Columbia, have invented a new and useful 'Improvement in Photometric Devices, and application for Letters Patent on said improvement is made under the act of Congress of March 3, 1883, cha ter 143:3. l

T e invention herein described may be used'by the United States Goverment, or' any of its officers or employees in prosecution of work for the Unlted States Government, or'by any other person in theUnited States, without the payment to me-of Aany royalty-thereon.

The following description in connection with the accompanying drawings is a full,` clear and exact specification of my im rovement, such aswill enableI those ski ed in the art to which it'appertains to make and use the same.

My invention relates to an inriprovementv -in such photometric devices as employ a pair of Nicol prisms inassociation with other polarizing optical parts. In devices ofthie kind the. ordinary law connecting the intensity and the anglebetween'corresponding planes in the two nicole 'cannotbe used as a formula for obtaining 'the intensity.` An 'exam leof such a case occurs in the path of t e beam of t passing through collimatorfB, Fig. 2, nited States Patent No. 1,026,878. In this caseint'ensity cannot be measured by the ordinary formula by rotating the analyzer, for the plane of polarization of the beam incident on the prism P is thus rotated' and the intensity of the beam relected from the prism is a func- Y tion of the angle between the plane of inci dence and the plane of polarization of the incident beam. The diculty can be obviated by rotating the polarize'r instead ofthe analyzer provided-the vbeam incident on the polarizer is known to be completely unpolar- .1zed.' It is in cases where this is not true device is not completely unpolarized and ,atj

the same time there are other polarizing optical Yparts succeeding the devlce in the ath of the light. To thls endl use three 1co1 prisms in train mounted in such a way that the rincipal planes ofthe two end nicols can. e suitably fixed with reference to other opxtical parts precedingl and succeeding the t ee nicols in the pat be rotate with reference .tov these planes. The law relat the intensity of the light and the a les tween Vthe just mentioned principal p anes can be definitely stated'and B5 used asa rmula for'measurements. 'In the preferred applicationof my invention the` anlebetween the principal planes of the en mcols is.zero and the intensity' is proportional tothe fourth power ofthe cosine v sistsin certain improvements and combina- 15 tions of parts all as will be herelnafter more fully described, the novel` feature being .pointed out in the claims at the end of the specification.

In the accompanying driiwings Figure 1 80) is a side elevation; certain parts being broken away, and Fi 24is a front elevation Y of a preferred embodlment of my invention. Fig. A3 is a diagrammatic view showing my device as used 1n connection with a deflect- .85'

ing surface.

1,2, and 3 represent three Nlcol prisms ada .ted to be disposed in axial alinement wit respect toeac other. To conveniently support these Nicol prisms in operative position I have mounted each in a .tube-'5 as is customary in devices of this kind. The tubes 5 are journaled inlarger tubes 4 and so associated therewith that they can beconveniently withdrawn, when desired; The tubes i are carried by posts 13 adapted for telescopic connection with hollow standards 14 whlch are preferably projecting from a base plate 15 so that the enumerated parts form a unitary structure. Tubes 13 and standards 100 14 are preferably. provided with a oove and tongue connection to admit of a owering and raising of theoptical parts without disturbin thelr axial allnement. As shown at the le along its bore agroove 16`a11d attached to the post 13 is a pin 17 adapted for free sliding movement 1n the groove 16. For the p ose of holding the post-131m any deof the light, while .60 ,the principal plane of the middle nicol can of Fig. 1 the standard 14 has 195 v position vertically of the standard M 110 i I have provided a set screw 12 carried by the standard 14 and adapted to impinge upon the post 13.

The standard 14 is preferably made in two parts, the lower part 18 having. a cylindrical bore and the upper tubular member 19 adapted to be received in the bore and to be freely rotatable therein. A set screw 20 is employed to fix the parts 18 and 19 in any desired relative position.. The parts 18 and 19 are suitably provided with abutments 21 and 22 to limit the rotative movement of the tubular member 19 and to constitute aready `means for adjusting the standards 14 together with the optical elements carried thereby to their operative position.

Aas "seen from an inspection of Fig. 1, I

' have made the central standard shorter and the device.

' attached on the outer tubes 4 to coperate with the scales for the purpose specified. I have made scale 7 and pointer 9 of slightly larger dimension than scale 6 and .pointer 8 to admit of la convenient reading vof the scales from rzone point. The ends of tubes 5 opposite the scales I have provided with screw threads to receive collars 10. These collars have shoulders to abut against the tubes 4 and to revent longitudinal motion of the inne`r tu es 5 relative tothe outer tubes 4. The tube 5 carrying prism 2 is held in place by two collars 1Q as shown in Fig. 1 and is`normally held* in fixed position with its principal plane normal to the base. The. scales and collars have central apertures 11 for the passageof the light. In Fig. -3 Ihave shown my device as used in connection with a reflecting surface simi- .lar to the arrangement in Fig. 2 of the Patent 1,026,878 above referred to. `My device is, however, by no means limited to that particular application and the relecting surface there shown is merely representative of such polarizing opt-ical parts, of whatever character they may be, as affect the accuracy of photometric measurements as above pointed out.

line of collimation of the other two prisms and the outer risms 2 and 3 are angularly adjusted relative to each other to any desired angle by turning prism 3 and scale 6. Ordinarily I prefer to have prisms 2 and 3 so adjusted that their principal planes are in parallelism which position would be indicated by the indicator 8 on the scale 6 pointing to zero. After the prisms 2 and 3 are properly adjusted, prism 1 is raised and brought into alinement with' prisms 2 and 3. In this position the device is ready for use. The intensity of a beam of light passing through the system is varied by turning the middle rism 1 and the angle of rotation of the mid le prism with respect to the relatively fixed outer prisms is a criterion of the intensity of the delivered beam.

While I have shown and described a speciic form of embodiment of my invention for the purpose of illustrating what I consider at present a preferred form, I do not wish to be limited to that particular form as it is obvious that my invention is susceptible of different forms of execution and such forms may vary to suit particular circumstances and conditions that might arise in the use of my device. It is furthermore to be understood that while I preferably dispoise the two end nicols in parallelism any other intermediate angle between ism and crossed prisms may be'use for the purposes for which the device is designed.

Having described my invention, what I claim' as new and desire to secure by Letters Patent is:

.1. In a device of the character described, the combination of three Nicol prisms, the

outer members of which are relatively stacipal planes and the inner member of which is rotatable and means for indicating the an ar relation of the pmnclpal plane thereof with respect to one of the outer prisms.

IRWIN G. PRIEST. Witnesses PHILIB O. WELLS, CHAUnoEY G. PETERS.

arallel- 

